A pneumatic atomizer is a device that uses a flow of gas to disperse a flowable liquid as small droplets. The present invention concerns an improved pneumatic atomizer for producing a fine dispersion of a flowable liquid in a gas. Several devices known for pneumatically atomizing a flowable liquid involve elements that produce a thin liquid filament or a thin liquid film and introduce the thin liquid filament or film to an adjacent high speed flow of gas. Examples of such devices include devices that:
(a) In accordance with the Erb and Resch U.S. Pat. No. 3,993,246 and Erb and Resch U.S. Pat. No. 4,018,387, liquid to be atomized is supplied between two elements, one of which is flexible and can be adjusted to provide a restricted outlet between the elements, the restricted outlet being in communication with a high speed flow of gas; PA1 (b) In accordance with the Erb and Resch U.S. Pat. No. 4,261,511, liquid to be atomized is supplied through shallow passages between two contacting elements, the outlet of the passages being in communication with a high speed flow of gas; and PA1 (c) In accordance with the Erb and Resch U.S. Pat. No. 4,161,281 and Erb and Resch U.S. Pat. No. 4,161,282, a controlled flow of the liquid to be atomized is supplied onto an exposed smooth surface that has an edge in communication with a high speed flow of gas whereby the liquid flows across the exposed surface as a thin film of liquid into the flowing gas.
All of such pneumatic atomizers involve an outlet orifice for the gas flowing through the atomizer, the gas outlet orifice passing through an exterior surface of the atomizer that is approximately perpendicular to the gas flow as the gas exits the gas orifice. An unavoidable consequence of gas flowing through a surface that is approximately perpendicular to the gas flow at the point where the gas exits the atomizer, as a gas eddy naturally forms just above the surface. The gas eddy surrounds the gas exiting the gas orifice, and this gas flows in a circular course. The gas in the gas eddy may thus be regarded as flowing in a course that commences in the gas flowing out of the atomizer at a place which is just downstream from the gas exit orifice, then flowing with the column of gas flowing out of the atomizer, then flowing perpendicular to the column of such gas, then flowing back toward the surface of the atomizer, then flowing across the surface of the atomizer to reenter the column of gas flowing out of the atomizer.
It is to be noted that the gas eddy has been the source of large droplets in the output of prior art pneumatic atomizers of the types described above, and for certain usages, such large droplets are undesirable. The gas eddy naturally contains gas from the column of gas flowing out of the atomizer. Such gas comes from the column of gas exiting the atomizer a short distance downstream in the gas flow from where the gas exited the atomizer and contains liquid droplets that were formed in the atomizer. It is to be realized that any liquid droplets that be in the gas that enters the gas eddy are carried into the gas eddy by such gas. The droplets are swept toward the atomizer by the gas in the eddy circulating back toward the atomizer. The gas circulating in the eddy toward the atomizer turns a short distance above the face of the atomizer to flow across the face of the atomizer towards the gas orifice, and as a consequence, many of the droplets in the circulating gas fly out of the eddy.
Quite a number of such droplets impact on the face of the atomizer around and about the gas orifice and any structural element of the atomizer that surrounds the face of the atomizer, such as the top plate in the aforementioned Erb and Resch Patents '281 and '282, wetting the face of the atomizer and any surrounding structural element.
The droplets collect as large droplets on the face of the atomizer and the surrounding structural element. Visually it appears as though the face of the atomizer and the surrounding structural element were sweating large droplets. The large droplets are swept by the gas flowing in the gas eddy toward the gas orifice and into the column of gas exiting the atomizer. The gas flowing out of the atomizer shatters the large droplets into small droplets when the large droplets come into contact with the gas flowing out of the gas orifice and carries the small droplets away within the column of gas leaving the atomizer. The droplets that are the result of the foregoing generally are not as small as the very small droplets initially formed by the atomizer.
The consequence of this is that the column of gas leaving the atomizer contains (a) the very small droplets initially formed by the atomizer and (b) the unwanted relatively large small droplets that are the result of the naturally occurring gas eddy.
It is the purpose of this invention to provide an atomizer that improves upon these results.